The trade-off between interest rate variability and the width of an exchange rate target zone is examined, using the regulated Brownian motion model of target zones. The interest rate differential’s asymptotic (unconditional) variability is increasing in the exchange rate band for narrow bands; whereas it is slowly decreasing for wide bands. The interest rate differential’s instantaneous (conditional) variability is decreasing in the exchange rate band. The model is extended to include a realignment/devaluation risk, as well as an endogenous exchange rate risk premium. The risk premium is small for reasonable parameter values.

This paper studies the Mexican and Israeli experience with a target zone. The first part of the paper develops a model of exchange rate determination under a target zone regime with stochastic realignments, and examines the conditions under which the adoption of the target zone, instead of a fixed exchange rate, reduces the volatility of the interest rate differential. We conclude that if the variance of the expected realignment is sufficiently large, then the target zone will be useful. The second part of the paper is an empirical study that shows that the target zone regime helped reduce interest rate variability in Israel and Mexico by absorbing part of the shocks to the expected realignment with movements of the exchange rate inside the band.

The term structure of interest rate differentials is derived in a model of a small open economy with a target zone exchange rate regime. The target zone is modeled as a regulated Brownian motion. The interest rate differentials are computed as the solution to a parabolic partial differential equation with derivative boundary conditions, both via a Fourier-series analytical solution and via a direct numerical solution. Several specific properties of the term structure of interest rate differentials are derived. For instance, for given time to maturity the interest rate differential is decreasing in the exchange rate, and for given exchange rate the interest rate differential's absolute value and its instantaneous variability are both decreasing in the time to maturity. Devaluation/realignment risks are incorporated and imply upward shifts of the interest rate differentials. Some implications of the theory are found to be broadly consistent with data on Swedish exchange rates and interest differentials for the period 1986-1989.